Methods and apparatus for phase selection in ring magnet sensing

ABSTRACT

Methods and apparatus for positioning a magnetic field sensor IC package having a first channel for a planar magnetic field sensing element and a second channel for vertical magnetic field sensing element in relation to an axis of a ring magnet to provide a desired phase relationship between the first and second channels. In embodiments, positioning the sensor includes an offset angle and a displacement with respect to a centerline of the ring magnet.

RELATED APPLICATIONS

This present application is continuation of U.S. patent application Ser.No. 14/950,104, titled “METHODS AND APPARATUS FOR PHASE SELECTION INRING MAGNET SENSING” filed Nov. 24, 2015, which is incorporated hereinby reference in its entirety for any and all purposes.

BACKGROUND

As is known, there are a variety of types of magnetic field sensingelements, including, but not limited to, Hall effect elements,magnetoresistance elements, and magnetotransistors. As is also known,there are different types of Hall effect elements, for example, a planarHall element, a vertical Hall element, and a circular Hall element. Asis also known, there are different types of magnetoresistance elements,for example, a giant magnetoresistance (GMR) element, an anisotropicmagnetoresistance element (AMR), a tunneling magnetoresistance (TMR)element, and a magnetic tunnel junction (MTJ).

Hall effect elements generate an output voltage proportional to amagnetic field. In contrast, magnetoresistance elements changeresistance in proportion to a magnetic field. In a circuit, anelectrical current can be directed through the magnetoresistanceelement, thereby generating a voltage output signal proportional to themagnetic field.

Magnetic field sensors, i.e., circuits that use magnetic field sensingelements, are used in a variety of applications, including, but notlimited to, a current sensor that senses a magnetic field generated by acurrent carried by a current-carrying conductor, a magnetic switch thatsenses the proximity of a ferromagnetic object, a rotation detector thatsenses passing ferromagnetic articles, for example magnetic domains of aring magnet, and a magnetic field sensor that senses a magnetic fielddensity of a magnetic field.

SUMMARY

The present invention provides methods and apparatus for positioning amulti-channel magnetic field sensor in relation to a ring magnet toachieve a desired electrical phase relationship for the sensor outputs.In illustrative embodiments, the magnetic field sensor is positioned tohave an offset angle, which can be referred to as ‘twist,’ with respectto a centerline of the ring magnet and a displacement of magnetic fieldsensing elements in the magnetic sensor from the center of the ringmagnet.

In one aspect of the invention, a method comprises: for a magnetic fieldsensor IC package having a first channel for a planar magnetic fieldsensing element and a second channel for a vertical magnetic fieldsensing element, receiving a desired phase relationship between thefirst and second channels; and positioning the IC package in relation toan axis of a ring magnet to provide the desired phase relationshipbetween the first and second channels.

The method can further include one or more of the following features:positioning the IC package to a non-zero twist angle with respect to theaxis and a non-zero displacement with respect to the axis, the axiscorresponds to a centerline of the ring magnet, the centerlinecorresponds to one half a width of the ring magnet, the desired phaserelationship is about 120 degrees, the desired phase relationship isabout 60 degrees, displacing the IC package position a distance from anaxis of rotation of the ring magnet, the IC package has a longitudinalaxis defined by being perpendicular to a sensing direction of the firstsensing element, wherein the twist angle is defined by the longitudinalaxis of the IC package and the centerline of the ring magnet, the phaserelationship is selected using a mesh function of the offset angle anddisplacement for the sensor, a substantially planar face of the ICpackage defines an air gap with a surface of the ring magnet, the planarmagnetic field sensing element and the vertical magnetic field sensingelement are formed as part of a single die, the planar magnetic fieldsensing element and the vertical magnetic field sensing element aresubstantially collocated, positioning the IC package to lessensensitivity to mechanical tolerances, and/or the first sensing elementcomprises a Hall element.

In another aspect of the invention, an apparatus comprises: a ringmagnet; and a magnetic field sensor IC package positioned in relation toa ring magnet to achieve a selected phase relationship between a firstchannel for a planar magnetic field sensing element and a second channelfor a vertical magnetic field sensing element.

The apparatus can further include one or more of the following features:the IC package is positioned to a non-zero twist angle with respect tothe axis and a non-zero displacement with respect to the axis, the axiscorresponds to a centerline of the ring magnet, the centerlinecorresponds to one half a width of the ring magnet, the desired phaserelationship is about 120 degrees, the desired phase relationship isabout 60 degrees, the IC package is positioned a distance from an axisof rotation of the ring magnet, the IC package has a longitudinal axisdefined by being perpendicular to a sensing direction of the firstsensing element, wherein the twist angle is defined by the longitudinalaxis of the IC package and the centerline of the ring magnet, the phaserelationship is selected using a mesh function of the offset angle anddisplacement for the sensor, a substantially planar face of the ICpackage defines an air gap with a surface of the ring magnet, the planarmagnetic field sensing element and the vertical magnetic field sensingelement are formed as part of a single die, the planar magnetic fieldsensing element and the vertical magnetic field sensing element aresubstantially collocated, and/or the IC package is positioned to lessensensitivity to mechanical tolerances.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of this invention, as well as the inventionitself, may be more fully understood from the following description ofthe drawings in which:

FIG. 1 is a schematic representation of a multi-channel magnetic fieldsensor positioned in relation to a ring magnet;

FIG. 1A is a schematic representation of the ring magnet and sensor ofFIG. 1;

FIG. 1B is a graphical representation of outputs of the magnetic fieldsensor of FIG. 1;

FIG. 2 is a schematic representation of magnetic field sensor havingplanar and vertical magnetic field sensing elements;

FIG. 3 is a graphical representation of electrical phase for offsetangle and displacement with respect to a ring magnet;

FIG. 3A shows a further graphical representation of electrical phase foroffset angle and displacement with respect to a ring magnet;

FIG. 3B shows a further schematic representation of a multi-channelmagnetic field sensor positioned in relation to a ring magnet;

FIG. 4 is a schematic representation of a magnetic field sensor and ringmagnet in a conventional arrangement;

FIG. 4A is a graphical representation of the sensor outputs for thearrangement of FIG. 4;

FIGS. 5A and 5B show positioning of a magnetic field sensor havingplanar and vertical magnetic field sensing elements in relation to aring magnet;

FIGS. 5C and 5D shows an alternative positioning of a magnetic fieldsensor having planar and vertical magnetic field sensing elements inrelation to a ring magnet;

FIG. 6 is a functional block diagram of an illustrative magnetic fieldsensor having planar and vertical sensing elements;

FIG. 7 is a flow diagram showing an illustrative sequence of steps forachieving a desired electrical phase relationship between first andsecond outputs of a multi-channel magnetic field sensor.

DETAILED DESCRIPTION

As used herein, the term “magnetic field sensing element” is used todescribe a variety of electronic elements that can sense a magneticfield. The magnetic field sensing element can be, but is not limited to,a Hall effect element, a magnetoresistance element, or amagnetotransistor. As is known, there are different types of Hall effectelements, for example, a planar Hall element, a vertical Hall element,and a Circular Vertical Hall (CVH) element. As is also known, there aredifferent types of magnetoresistance elements, for example, asemiconductor magnetoresistance element such as Indium Antimonide(InSb), a giant magnetoresistance (GMR) element, for example, a spinvalve, an anisotropic magnetoresistance element (AMR), a tunnelingmagnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ).The magnetic field sensing element may be a single element or,alternatively, may include two or more magnetic field sensing elementsarranged in various configurations, e.g., a half bridge or full(Wheatstone) bridge. Depending on the device type and other applicationrequirements, the magnetic field sensing element may be a device made ofa type IV semiconductor material such as Silicon (Si) or Germanium (Ge),or a type III-V semiconductor material like Gallium-Arsenide (GaAs) oran Indium compound, e.g., Indium-Antimonide (InSb).

As is known, some of the above-described magnetic field sensing elementstend to have an axis of maximum sensitivity parallel to a substrate thatsupports the magnetic field sensing element, and others of theabove-described magnetic field sensing elements tend to have an axis ofmaximum sensitivity perpendicular to a substrate that supports themagnetic field sensing element. In particular, planar Hall elements tendto have axes of sensitivity perpendicular to a substrate, while metalbased or metallic magnetoresistance elements (e.g., GMR, TMR, AMR) andvertical Hall elements tend to have axes of sensitivity parallel to asubstrate.

As used herein, the term “magnetic field sensor” is used to describe acircuit, which can be provided in an IC package, that uses a magneticfield sensing element(s), generally in combination with other circuits.Magnetic field sensors are used in a variety of applications, including,but not limited to, an angle sensor that senses an angle of a directionof a magnetic field, a current sensor that senses a magnetic fieldgenerated by a current carried by a current-carrying conductor, amagnetic switch that senses the proximity of a ferromagnetic object, arotation detector that senses passing ferromagnetic articles, forexample, magnetic domains of a ring magnet or a ferromagnetic target(e.g., gear teeth) where the magnetic field sensor is used incombination with a back-biased or other magnet, and a magnetic fieldsensor that senses a magnetic field density of a magnetic field.

FIG. 1 shows a system 100 including a multi-channel magnetic fieldsensor 102 positioned in relation to a ring magnet 104. The magneticfield sensor 102 can sense magnetic fields orthogonal to one another.The sensor 102 is offset at an angle from a centerline of the ringmagnet 106 and displaced from the centerline, as described more fullybelow. In embodiments, the centerline 106 corresponds to the middle ofthe width w of the ring magnet 104. The ring magnet 104 refers tomagnetic material, such as permanent magnets.

The ring magnet 104 has a number of pole pairs (npp) forming a radialmagnetization. The ring magnet 104 has an outer diameter OD and an innerdiameter ID (FIG. 1A), which corresponds to a shaft 108 of the ringmagnet. It is understood that in embodiments, the ring magnet has an IDof 0 mm such that the magnet could be press fit or glued to the end of arotating shaft, for example. A distance R is the distance between arotation axis 110 of the shaft and sensing elements 112 of the magneticfield sensor 102. A displacement d refers to the distance between thecenterline 106 of the ring magnet and the location of the magnetic fieldsensing elements 112 of the magnetic sensor 102. In embodiments, themagnetic field sensing elements are aligned with the rotation axis 110of the ring magnet. In the illustrated embodiment, the twist/offsetangle α is about 30 degrees and the displacement d is about 4 mm. In oneembodiment, the centerline 106 of the ring magnet is defined by a widthw of the ring magnet 104. For a displacement of d=0, the magnetic fieldsensing elements 112 of the sensor are aligned with the centerline 106of the ring magnet.

In general, ring magnets have ninety degrees of phase shift betweenplanar and vertical fields. The magnetic field sensor 102 is offset anddisplaced from the centerline of the magnet 104 for modifying the phasebetween the sensor outputs to a desired amount. By ‘twisting’ theposition of the sensor 102, the angle in which the vertical Hall elementfaces the ring magnet 104 is altered. When the twist angle α is greaterthan 0 degrees, there is y axis rotation in a z axis direction, as canbe seen. In embodiments, the offset or twist angle α is defined by alongitudinal axis 103 of the IC package through the magnetic fieldsensing elements with respect to the ring magnet centerline 106. It isunderstood that the longitudinal axis 103 is defined by one of thesensing elements 112 within the IC package, and more particularly, anaxes of sensitivity of a sensing element.

FIG. 2 shows longitudinal axis 103 defined by the axis of sensitivity ofthe first sensing element 202. Thus, the twist angle α in relation tothe first sensing element is such that the sensor is rotated in the XY/Z plane around the X axis for the illustrated embodiment. It isunderstood that the sensor rotates such that the distance R (FIG. 1A)from the center 110 of magnet rotation is constant for all points of thesensing element.

In embodiments, longitudinal axis 103 is defined by a sensitivity axisof one sensing element. In the embodiment of FIG. 2, axis 103 is definedby the first sensing element 202 sensing along Y, for example, where theaxis 103 is parallel to the sensing direction of the first sensingelement 202. In the illustrated embodiment, the field measured by thesecond sensing element 204 is independent of the sensor twist angle α,sensing direction being X. It is understood that the sensing elementsare generally fixed in position within the IC package. Thus, alongitudinal axis of an IC package defines the axis in relation to theposition of the sensing element(s) within the IC package.

For example, should an application require a nominal phase shift betweenchannels of 120 degrees, the sensor is twisted and displaced such thatthe sensor outputs have an electrical phase relationship of 120 degreesinstead of the nominal 90 degrees. It is understood that a wide range ofphase relationships can be desired to meet the needs of a particularapplication.

FIG. 1B shows illustrative signals for first and second outputs Bx, Byof the magnetic sensor with a phase offset of about 60 mechanicaldegrees, e.g., 89.9-28.8. As can be seen, digital output By rises atposition X:28.8, Y:0 and digital output Bx rises at X:28.8, Y:0. Thisphase relationship between the outputs is achieved by an illustrativeoffset angle α of about −30 degrees and a displacement of about 4 mm.

FIG. 2 shows an illustrative magnetic field sensor 200 having a verticalHall element 202 that is sensitive to magnetic fields in a planeparallel to a die face, shown as the y dimension, and a planar Hallelement 204 that is sensitive to magnetic fields in a planeperpendicular to the die face, shown as the x dimension. The planar hallelement 204 is sensitive in the X axis (into the paper in theillustrated embodiment), and the vertical hall element 202 is sensitivein the y axis. As described above, the axis 103 defined by one of thesensing elements defines the twist angle α in relation to the ringmagnet centerline 106 (FIG. 1).

FIG. 3 shows the electrical phase of the first and second outputs of themagnetic field sensor varying by twist angle α and displacement d inrelation to a ring magnet. With zero twist angle, it can be sees thatphase is virtually fixed at 90°. The same holds if the sensing elementposition is aligned with the ring magnet centerline (d=0) and the deviceis twisted. In order to see the effect of the twist angle α on the phaserelationship, there must be a displacement d of the sensor from the ringmagnetic centerline.

As can be seen, electrical phase relationship of the sensor outputscorresponds to the twist angle α and displacement d. The pointhighlighted (X: −30, Y:4, Z:122.2) shows that with −30° of twist angle,and displacement d of 4 mm, ˜120° of phase separation is achieved.Twisting the sensor in the opposite direction (+30°) results in a phaseshift of ˜60°). As will be appreciated, there are a number of α and dsolutions for a desired phase relationship. That is, for a given targetphase shift, there is a set of solutions that exist along the lineresulting from the intersection of a plane located at the specifiedphase, and the resulting illustrated mesh function of α and d.

FIG. 3A shows a further mesh function representation of electrical phaseφ of the first and second outputs of the magnetic field sensor withsensor positioning in the y and z dimensions in relation to a ringmagnet for optimizing a position of the sensor along y axis (consistentwith the y-axis of FIG. 1). This allows a user to determining sensorpositioning that is less sensitive to mechanical tolerances.

For example, a desired electrical phase φ is 60 degrees. For theselected point [Y:5, Z:3, φ:60] the displacement d corresponds to Zshift axis. The sensor twist angle α is fixed at 40°. There is also a 5mm shift in sensor position on the Y axis.

FIG. 3B shows a sensor 300 positioned in relation to a ring magnet 302with a twist angle α of about 20 degrees, a displacement d from the ringmagnet centerline 304, and a y-axis displacement e, which is defined inrelation to a location of the a sensing element and a rotation axis ofthe ring magnet 302.

While illustrative embodiments are shown and described in conjunctionwith dual channel magnetic field sensors, it is understood that anypractical number of channels and magnetic field sensing elements can beused to meet the needs of a particular application.

FIG. 4 shows a conventional arrangement 400 of a dual channel magneticfield sensor 402 and ring magnet 404 with no twist, i.e., α=0, and nodisplacement, i.e., d=0 and e=0. The sensor 402 has first and secondoutputs with the sensor sensing along x and y axis with distance d=0 andα=0°. FIG. 4A shows the sensor outputs for the arrangement for FIG. 4 ina conventional ninety degree phase offset between the first and secondoutput channels. The ring magnet has 2 pole pairs and w=10 mm. As can beseen in FIG. 4A, the mechanical phase shift between the first and secondoutputs is 45°. This is equivalent to a 90° electrical phase shift,e.g., electrical phase shift=npp*mechanical phase shift. This is theconventional behavior of a 2D sensor having a 90° shifted sensing axis.

In an illustrative embodiment, the magnetic field sensor comprises aHall-effect latch for sensing planar and vertical magnetic fielddirections. The dual operation of the planar and vertical Hall elementsallows the end user to achieve phase separation that is independent ofmagnetic pole spacing on the ring magnet. The sensor channel outputsallow rotation direction to be determined, such as when sensing arotating ring-magnet target.

In illustrative embodiments, a dual channel two dimensional Hall Effectlatch-type magnetic field sensor is positioned in relation to a ringmagnet to effect the desired phase relationship of the sensor outputsignals. In embodiments, sensor outputs switch low (turn on) when asouth polarity magnetic field perpendicular to the Hall-effect sensorexceeds the operate point threshold (BOP). In other embodiments, asensor provides a continuous analog output with phase separation.

As shown in FIGS. 5A-D, the sensor package can be configured to detect avariety of magnetic field orientations. FIGS. 5A and 5B shows a sensorpackage having a planar Hall element and a vertical Hall element forsensing magnetic fields when the package faces the ring magnet (FIG. 5A)or when a leaded side of the package faces the ring magnet (FIG. 5B).FIGS. 5C and 5D show magnetic field detection for a sensor packagefacing the ring magnet (FIG. 5C) or a non-leaded side of the packagefacing the ring magnet (FIG. 5D). It is understood that the sensor canhave various twist angles and displacement, as described above, toachieve a desired phase relationship for the sensor output signals.

FIG. 6 shows an illustrative functional black diagram of a dual channelmagnetic field sensor 600 that can be positioned in relation to a ringmagnet to achieve a desired phase relationship of the sensor outputs. Inembodiments, a magnetic field sensor comprises a single silicon die witha planar Hall plate (Z) and a vertical Hall plate (X/Y). The Hall platesare coupled to a module 602 providing dynamic offset cancellation andmultiplexing. The module 602 output is coupled to a small-signalamplifier 604, a low pass filter 606, a sample, hold, and averagingmodule 608, a Schmitt trigger 610, a demultiplexer 612 and respectiveshort-circuit protected NMOS output transistors TX1, TX2 to provideoutput A and output B. It is understood that the axes used herein arenot intended to refer to any global position, but rather to definepositions of one thing in relation to another.

FIG. 7 shows an illustrative sequence of steps for achieving a desiredelectrical phase relationship between outputs of a multi-channelmagnetic field sensor. In embodiments, the magnetic field sensor isprovided in an IC package containing a planar magnetic field sensor anda vertical magnetic field sensor. In step 700, a ring magnet having agiven number of pole pairs is provided. In illustrative embodiments, thering magnet has a width defining a centerline and an axis of rotation.In step 702, a desired electrical phase relationship between outputs ofthe multi-channel sensor is received. In step 704, an offset angle αdefined by the sensor and magnetic field sensing elements is determinedand in step 706 a displacement d of the magnetic field sensing elementsfrom the ring magnet centerline is determined. In optional step 707, adisplacement e can be determined. It is understood that the offset angleα and displacement d together define the phase relationship. That is,there is no sequence for offset angle α and displacement d. In oneembodiment, the offset angle α and displacement d are selected from amesh function relating electrical phase to the offset angle α anddisplacement d. For example, a desired phase of 120 degrees can beachieved by selecting a solution of α and d from the mesh function andpositioning the sensor in relation to the ring magnet accordingly instep 708. It is understood that a user can perform an analysis toevaluate tradeoffs for achieving a target phase margin performance. Forexample, points located on steeper parts of the curve, may be moresensitive to assembly tolerance, vibration, magnetic target wobble, andthe like, such as parameter e.

While illustrative embodiments of the invention are shown and describedin conjunction with dual channel latch-type, Hall Effect magnetic fieldsensors, it is understood that any suitable type sensor having asuitable type of magnetic field sensor, such as those listed above, canbe used.

Having described exemplary embodiments of the invention, it will nowbecome apparent to one of ordinary skill in the art that otherembodiments incorporating their concepts may also be used. Theembodiments contained herein should not be limited to disclosedembodiments but rather should be limited only by the spirit and scope ofthe appended claims. All publications and references cited herein areexpressly incorporated herein by reference in their entirety.

Elements of different embodiments described herein may be combined toform other embodiments not specifically set forth above. Variouselements, which are described in the context of a single embodiment, mayalso be provided separately or in any suitable subcombination. Otherembodiments not specifically described herein are also within the scopeof the following claims.

What is claimed is:
 1. A method, comprising: for a magnetic field sensorIC package having a first channel for a planar magnetic field sensingelement and a second channel for a vertical magnetic field sensingelement, receiving a desired phase relationship between the first andsecond channels; and positioning the IC package in relation to an axisof a ring magnet to provide the desired phase relationship between thefirst and second channels.
 2. The method according to claim 1, furtherincluding positioning the IC package to a non-zero twist angle withrespect to the axis and a non-zero displacement with respect to theaxis.
 3. The method according to claim 1, wherein the axis correspondsto a centerline of the ring magnet.
 4. The method according to claim 3,wherein the centerline corresponds to one-half a width of the ringmagnet.
 5. The method according to claim 1, wherein the desired phaserelationship is approximately 120 degrees.
 6. The method according 1,wherein the desired phase relationship is approximately 60 degrees. 7.The method according to claim 1, further including displacing the ICpackage position a distance from an axis of rotation of the ring magnet.8. The method according to claim 1, wherein the IC package has alongitudinal axis defined by being parallel to a sensing direction ofthe first sensing element, wherein the twist angle is defined by thelongitudinal axis of the IC package and a centerline of the ring magnet.9. The method according to claim 1, further including determining anoffset angle with relation to the axis based upon the desired phaserelationship.
 10. The method according to claim 9, wherein positioningthe IC package in relation to an axis of a ring magnet to provide thedesired phase relationship between the first and second channelscomprises positioning the IC package in relation to the axis accordingto the determined offset angle.
 11. The method according to claim 1,wherein a substantially planar face of the IC package defines an air gapwith a surface of the ring magnet.
 12. The method according to claim 1,wherein the planar magnetic field sensing element and the verticalmagnetic field sensing element are formed as part of a single die. 13.The method according to claim 1, wherein the planar magnetic fieldsensing element and the vertical magnetic field sensing element aresubstantially collocated.
 14. The method according to claim 1, furtherincluding positioning the IC package to lessen sensitivity to mechanicaltolerances.
 15. The method according to claim 1, wherein the firstsensing element comprises a Hall element.
 16. An apparatus, comprising:a ring magnet; and a magnetic field sensor IC package positioned inrelation to a ring magnet to achieve a desired phase relationshipbetween a first channel for a planar magnetic field sensing element anda second channel for a vertical magnetic field sensing element.
 17. Theapparatus according to claim 16, wherein the IC package is positioned toa non-zero twist angle with respect to the axis and a non-zerodisplacement with respect to the axis.
 18. The apparatus according toclaim 16, wherein the axis corresponds to a centerline of the ringmagnet.
 19. The apparatus according to claim 18, wherein the centerlinecorresponds to one half a width of the ring magnet.
 20. The apparatusaccording to claim 16, wherein the desired phase relationship is about120 degrees.
 21. The apparatus according 16, wherein the desired phaserelationship is about 60 degrees.
 22. The apparatus according to claim16, wherein the IC package is positioned a distance from an axis ofrotation of the ring magnet.
 23. The apparatus according to claim 16,wherein the IC package has a longitudinal axis defined by beingperpendicular to a sensing direction of the first sensing element,wherein the twist angle is defined by the longitudinal axis of the ICpackage and the centerline of the ring magnet.
 24. The apparatusaccording to claim 16, wherein a substantially planar face of the ICpackage defines an air gap with a surface of the ring magnet.
 25. Theapparatus according to claim 16, wherein the planar magnetic fieldsensing element and the vertical magnetic field sensing element areformed as part of a single die.
 26. The apparatus according to claim 16,wherein the planar magnetic field sensing element and the verticalmagnetic field sensing element are substantially collocated.
 27. Theapparatus according to claim 16, wherein the IC package is positioned tolessen sensitivity to mechanical tolerances.